A common method of pumping fluids involves employing an internal or external gear set. The operating principal of the gear set is that as the volume of fluid changes with gear motion, a pressure differential is created which produces fluid flow. There are several pumps available in the market that utilize this technique. The two major types of gear pumps include spur gears (external) and rotor gears (internal).
A common problem with using these elements as the driving force is that they have difficulty compressing air. Prior to installing the pump onto a reservoir of fluid, the pump is filled with air. In order to allow the system to prime, the pump must displace this air to create the pressure differential previously mentioned. The most prevalent method of overcoming this issue is handled by having the end user dismantle a portion of the pump and pour a higher density fluid into the gear set housing, eliminating the requirement of compressing air. This will provide a compression ratio that is large enough to allow the pump to prime.
There are some disadvantages to this method. There is extra work and inconvenience required by the end user to take the pump apart, pour fluid into the gear housing and re-assemble the pump. In eases where dismantling the pump is not required, the pump requires long periods of time to prime. The extended period of time to prime decreases the life of the pump as the gears see increased wear when running without lubrication. Also gear pumps are typically sensitive to debris, which can cause leak paths and reduce pump performance. The requirement, to dismantle in the field could continue to increase, the possibility of the above-mentioned problems.